1. Field of the Invention
The invention relates to a micro-fabrication resist material which can readily be polymerized and insolubilized and to methods of using this resist material.
2. Description of the Prior Art
Micron order fabrication represented by IC's and LSI's is ordinarily conducted by photo-lithography using a photo resist. However, ultra-fine fabrication on a sub-micron order recently has been needed, making it impossible to use photo-lithography employing photo-resist. Therefore, studies were begun on the resist material and on lithography utilizing electromagnetic radiation with short wavelengths such as electron beams and X-rays, replacing the use of near ultraviolet and ultraviolet light. Use of this resist material is similar to use of a photo-resist and the procedure is described as follows. The substrate surface is coated with the resist material and a thin layer of a polymer is formed on the substrate surface by evaporating the solvent. The coated substrate is then exposed to electromagnetic radiation such as electron beams, X-rays or deep ultraviolet light and the polymer is cross linked and as a result insolubilized in the exposed portion. When in the next step the substrate is developed with an appropriate solvent, the exposed portion of the polymer layer remains and the unexposed portion of the polymer is washed away. The above-described resist material is usually categorized as a negative-type resist material. The resist material of this invention is a negative type resist material. The substrate having thereon the insoluble resist is subjected to doping, metallizing, and etching processing, etc. The fabrication process is completed by removing the resist with a solvent or plasma ashing.
As is evident from the fabrication method described above, the resist material must be have sufficiently high photoproperties such as sensitivity, contrast, resolution, edge sharpness, must be adhesive to the substrate and resistant to the ethchant and must have sufficient shelf life. Furthermore, the resist material should preferably not be so photo-sensitive that it must be processed in dark room. The resist material of this invention shows a high sensitivity to electromagnetic radiation of a wavelength less than about 3000 A, such as electron beams, X-rays, deep ultraviolet light (wavelength of approximately 2700 A to 1500 A). It is of value to mention here that the hitherto known negative type resist materials are decomposed by deep ultraviolet light irradiation resulting in a poor positive image. On the other hand, the resist material of this invention provides a very clear negative image as shown in the examples given hereinafter.
Sensitivity of the resist material is indicated by the dose of electromagnetic radiation required to insolubilize the resist material in the case of a nega-type resist material. In case of electron-beams that are most often utilized, contrast (.gamma.) is attained at (.gamma.=1 or above) supposing D.sup.i as the minimum dose for starting insolubilization and D.sup.o as a sufficient dose for 100% insolubilization. In order to permit a resist material to be used practically, D.sup.o .ltoreq.10.sup.-6 coulomb/cm.sup.2 and contrast.gtoreq.1 are ideal. A study of lithography using electromagnetic radiation (mainly electron beams) began in the last half of the 1960's. The resist material utilized initially was a common photo-resist. A photo-resist was an appropriate material for evaluation because its basic characteristics such as electro-sensitivity, adhesiveness to a substrate such as a silicon wafer, coatability, and resistance to etchants were sufficiently high. However, the properties of such a photo-resist were insufficient for electron beams, X-rays or deep ultraviolet light lithography to be put into practice. For instance, the sensitivity of a negative type photo-resist to electron beams was low, i.e., D.sup.o &gt;10.sup.-5 and this low sensitivity was a decisive disadvantage for spot scanning of electron beams which was used for mask production with a CAD. Around 1970, electron beam resist materials were announced. Among the many electron beam resist materials, a highly sensitive resist material with a D.sup.o approaching on the order of 10.sup.-8 coulomb/cm.sup.2 was developed. Such, however, had inferior contrast and was totally unsuitable for practical use. A photo-resist of another type, despite its good sensitivity and contrast, did not become practical due to difficulty in synthesis. A photo-resist material for submicron fabrication which is suitable for practical use has yet to be developed.